Radioactive source holder and shielding container



EEO-15.305191 ma ENUM@ June 2, 1955 J. c. PENNocK ETAL 2,711,485

RADIOACTIVE SOURCE HOLDER AND SHIELDING CONTAINER Filed Feb. 28. 1951 United States RADIOACTIVE SUURCE HOLDER AND SHIELDNG CONTAINER John C. Pennock, Marbiehead, and Albert J. Bacchieri, Dedham, Mass., assignors to Tracerlab, inc., Boston, Mass., a corporation of Massachusetts Original application February 28, 1951, Seria! No. 213,174, now Patent No. 2,670,443, dated February 23, 1954. Divided and this appiication May 3, 1952, Serial No. 285,946

The portion of the term of the patent subsequent to February 23, 1971, has been disciaimcd 10 Ciaims. (Cl. Z50-105) This invention relates to devices for forming a beam of radiant energy which may be used for the treatment of disease or the radiography of structural materials or the like and is a division of our copending application Serial No. 213,174, tiled February 28, 1951, which issued on February 23, 1954, as U. S. Patent No. 2,670,443. More particularly the invention is concerned with a new and improved radiant energy beamaforming device in which a radioactive source is removably mounted in a shield of radiation absorbing material with provision for producing an opening in such material to form a collimated beam of radiations and embodying new and improved means permitting the simple and safe loading into the shield and unloading therefrom of the radioactive source.

Devices for the purpose stated above have been used for a number of years with radium as the source of radiation. Because of the great cost of this rare material and f the inherent limitation on the amount of radiation which can be obtained from a naturally radioactive source of given size (volume specific activity), such devices have never been built to handle more than about 50 grams of radium.

Beam forming units using radium sources of 1 to 20 grams have usually consisted of a pneumatic device for transporting the source from a shielded storage container, which protects the attendant personnel from irradiation, to a collimating device and then back to the shielded storage container. While such a pneumatic transport system is satisfactory for handling radiation sources of limited strength, the possibility of jamming of the source in the transport tube in a position in which the operators will be unprotected makes such a device extremely hazardous for use with very high intensity radio-isotopes.

In order to arrive at some estimate of the potential danger inherent in the use of very high intensity gammaray sources, a comparison is given of the time required to receive a mean-lethal-dose (assumed to be 250 roentgens over the whole body) of gamma-radiation from a 50 gram radium source and from a 1000 curie and a 10,000 curie cobalt-60 source if the entire body is exposed at a distance of one meter from the source.

Lethal exposure table Source Time Required Approximately 6 hours. Approximately 11 minutes. Approximately 1.1 minutes.

50 Gram Radium 1,000 Curie Cobalt-60... 10,000 Curie Cobalt-60 'ice able and will become increasingly available in the form of materials which have been made artificially radioactive by exposure to neutrons in a nuclear reactor. Such material can be made with a much higher rate of emission of radiant energy per unit volume of source (higher specific activity) than is possible with radium, or other naturally radioactive materials, and at a much lower cost per unit of radiant energy. It is, therefore, now possible and economically practical to produce and use radiation sources with gamma-ray emission equivalent to thousands of grams of radium.

Several mechanisms which may be used to form collimated beams of radiations by moving a radioactive source into position in line with a hole in surrounding radiation absorbing material have been suggested. All of these devices, so far as we are aware, have three major disadvantages: First, they require power of some sort to shift the source from the beam-forming to the completely surrounded position with the attendant hazard of the source remaining in the beam-forming or some intermediate position for longer than is safe because of power failure. Second, to produce a beam of predictable shape and direction with a movable source, the latter must always be shifted to exactly the same location for forming the beam, thus requiring expensive and highly precise control equipment. Third, the problems of protection of personnel during the loading of a radioactive source into a device of the type which requires that the radioactive source be subsequently moved during operation are much more ditlicult of solution than the comparable problems with a device in which the source remains fixed after it has been once loaded.

The invention has tor its primary object the overcoming of the foregoing difficulties by providing a device for fomring a collimated beam of penetrative radiations in which the source is not shifted during use but which makes provision for the easy initial loading and subsequent unloading of the radioactive source while minimizing danger to the operating personnel.

Another object of the invention is to provide an improved radioactive source holder adapted for use with a beam-forming device of the type described.

Still another object of the invention is to provide a sim'- ple and safe radioactive source holder and container therefor permitting direct transfer of the source to the beam-forming unit without danger of the source becoming stuck in an unshielded position.

With the foregoing objects in mind a feature of the invention is the provision of a novel radioactive source holder comprising a rod of radiation absorbing material arranged to hold a radioactive source at a location spaced from its ends whereby radiations escaping from the source will be shielded by said material in directions axial of the rod, the rod being adapted to be inserted bodily in a shielding radiography container.

Another feature of the invention is the provision, in combination, of such a rod-like source holder and a novel shielding radiography container for said holder comprising a block of absorbing material having an aperture into which the holder may be readily loaded and a collimating slot and shutter arrangement, the slot extending into the aperture at the location of the source when the latter is in its inserted position, whereby radiations from the source will be absorbed by the material of the holder in directions axial of the holder and by the container and shutter, when closed, in all other directions or, when the shutter is open, formed into a beam collimated by said slot.

With the foregoing objects, features and advantages in View, the invention consists of the novel combination and arrangement of parts as disclosed in the following detailed description taken in connection with the accompanying drawings which disclose a preferred embodiment thereof and in which like numerals refer to like parts in the several views, and in which:

Fig. 1 is an elevation with portions cut away of the novel source holder of the invention; and

Fig. 2 is a fragmentary representation illustrating the manner of loading the source holder into the shielding sphere of a suitable radiography container according to the invention.

In the preferred embodiment here disclosed, the device consists of a shielding sphere in which is mounted a shutter 12 which is pivotally mounted on the shielding sphere 10 by any suitable means (not shown) so as to be movable from an open to a closed position. A suitable shutter arrangement including novel fail-safe features is disclosed in our co-pending application, Serial N o. 213,174, tiled February 28, 1951, of which the present application is a division. The shutter 12 may be operated by any suitable mechanism to move between the closed position, in which it is shown in Fig. 2, and an open position in which it leaves unblocked the collimating slot 13.

The shielding sphere 10 is constructed of a suitable structural material which also has the property of strongly absorbing radiations emanating from the source used, in this case gamma-rays. Such a material as tungsten or an alloy containing a high percentage of tungsten is suitable. The shielding sphere 10 may alternatively be constructed of a sturdy shell which may be permeable to gamma rays but which is filled with another material which has the property of strongly absorbing such rays. Such combination of materials as a steel shell filled with lead is suitable.

The shutter 12, like the shielding sphere 10, is constructed of a strong material which is relatively impermeable to the passage of gamma rays. Again, like the shielding sphere 10, the shutter 12 may comprise a shell of a radiation permeable material having good structural properties surrounding a core of another material having good absorption characteristics. It is not necessary to the invention that the same material or combination of materials be used in the shutter as is used in the sphere.

The shutter 12 is so shaped that it fits closely into the slot 13 with only suliicient clearance between its surfaces and the walls of the slot to allow ready opening and closing thereof. Further, the shutter 12 is of sufficient height and length that when it is in the closed position. as shown in Fig. 2, it mates with the slot 13 in such a way that any radioactive source at the center of the sphere will be shielded on all sides by suiiicient thickness of gamma ray absorbing material to reduce the radiation intensity at or near the surface of the shutter to a tolerable level.

The axle 1S is a hollow shaft passing through and rmly attached to the shielding sphere 1) and protruding from the sides of the same to form trunnions by which the entire device may be pivotally supported on hangers 16a and 16b. Other members of the mounting system have not been illustrated in detail since they do not form part of the present invention. The axle is partially cut away near the center of the sphere to form an opening 19 which is a continuation of the slot 13 and receives the shutter 12. Thus no portion of the wall of the axle 18 will interfere with the free passage through the slot 13 of gamma radiation from a source located at the center of the sphere 1t). The axle 18, therefore, not only furnishes trunnions for pivotally supporting the entire device but also provides an opening for receiving the radioactive source holder 22.

The hanvers 16a and 16h may be attached to any solid foundation such as the ceiling, walls, or iioor of a room. These hangers may be so arranged that translational motion of the device can be produced in any direction.

Referring to Fig. 1, the source cylinder 22 is a relatively strong metallic container having thin walls 26 with an outside diameter nearly equal to the inside diameter of the axle 18 but suiiiciently smaller to permit free sliding motion therewithin without danger of binding. The radio-active source 28 is preferably a capsule which fits inside the cylinder 22 and which contains the radioactive material which emits the gamma ray beam. The source 28 is positioned in the center of the cylinder 22 between the two plugs 3? which are composed of a material highly absorptive of gamma rays and which are fitted closely within the shell 26 of the source cylinder 22 and serve to prevent the escape of gamma rays from the source in an axial direction.

The unique manner of loading the radioactive source into the shielding sphere 10 is indicated in Fig. 2. The source 28 and the source cylinder plugs 30 have previously been loaded into the holder 22 in a working area provided with the necessary safeguards and remote handling equipment. The source cylinder 22 is then transported to the beam-forming unit in the auxiliary shielding container 24 which is made of a suitable radiation absorptive material and is provided with a cylindrical opening exactly fitting the holder 22.

The container 24 may have any convenient shape provided only that it provide suiiicient thickness of absorbing material to reduce the intensity of radiation at its surface to a tolerably low level. ln order to load the radioactive source 28 into the beam-forming unit, the internal bore of the axle 18 is aligned with the corresponding opening in the auxiliary container 24 and the cylinder 22 is pushed from one container into the other by means of a ram 32 having a handle 34. Thus, the radioactive source 28 is always Surrounded by sufcient absorbing material to reduce the radiation intensity to a level which is tolerable to the people near it except for the moment when the source proper is actually passing from the container 24 into the open end of the axle 18. If desired, it is possible to provide additional gamma ray absorbing material surrounding the space between the beam-forming unit and the auxiliary shielding container 24 to reduce the radiation intensity in the surrounding area during the moment of loading. Even if no such additional protection is provided, however, the persons who are doing the loading are to a great extent protected by interposing the auxiliary shielding container 24 between their persons and the source during the moment of loading. It it is desired to remove the radioactive source 28 for replacement or to facilitate maintenance of the beamforming unit, the above procedure is reversed and the rod 22 is pushed from the beam-forming unit into its seat in the carrying container 24. Both ends of the axle 18 may be closed by covers 20 (only one of which is shown) except during loading and unloading.

It Vvwill be understood that when the holder 22 is in place in the sphere 1t) the source 28 will be located opposite the collimating slot 13 and the corresponding opening 19 in the axle 18.

The device of the invention has been illustrated as adapted for use with a strong emitter of gamma rays, such as cobalt-60 since for therapeutic and radiographical purposes such raditaion, at present, appears to have the greatest practical value. It will be understood, however, that modifications and changes, primarily as to the nature of the absorbing material employed in the shielding members, will be readily apparent to those skilled in the art to adapt the unit for use with other radioactive sources emitting predominantly other types of penetrative radiations. For example, sources of neutrons might be employed, necessitating the employment of parain or other material of like characteristics in the shield.

Still other modifications and changes may occur to those skilled in the art within the spirit and scope of the appended claims.

Having described our invention, we claim:

l. In a unit for forming a beam of penetrative radiations from a radioactive source, the combination which comprises a generally spherical shield of radiation absorbing material, a hollow axle extending through said shield with the ends thereof protruding on either side of said shield to form trunnions for rotatably mounting the same, the opening in said axle being adapted to receive a radioactive source held in an elongated source holder fitting said opening, said shield and axle having matching slots forming a single collimating slot extending radially outwardly from the position of said source when in inserted position to an external surface of said shield.

2. In a unit for forming a beam of penetrative rad.'- ations from a radioactive source, the combination which comprises a generally spherical shield of radiation absorbing material, a hollow axle extending through said shield with the ends thereof protruding on either side of said shield to form trunnionsfor rotatably mounting the same, an elongated source holder removably insertable in said axle, said holder being composed of radiation absorbing material and having a source holding portion spaced from its ends for holding a radioactive source, the quantity of material between said source holding portion and both ends of said holder being sufficient to reduce the intensity of radiations passing therethrough in an axial direction to a tolerable level, said shield and axle having a collimating slot extending from an exterior wall into said axle at the location of said source holding portion of said holder' when said holder is in place inside said axle, and a shutterffor/said slot composed of radiation absorbing material.

3. In a unit for forming a beam of penetrative radiation from a radioactive source, the combination which comprises a shielding member of radiation absorbing material, a hollow axle extending through said shielding member with the ends thereof protruding on either side of said member, the opening in said axle being adapted to receive an elongated radioactive source holder fitting said opening, said shielding member and axle having matching slots forming a single collimating slot extending outwardly from the position of said source when in inserted position to an external surface of said shielding member.

4. A beam forming unit comprising, in combination, a generally spherical shielding member formed of radiation absorbing material having a central bore extending therethrough, an elongated source holder re.- movably positioned in and fitting said bore and being substantially coextensive therewith, said holder being composed of radiation absorbing material and having a radioactive source positioned intermediate its ends, said shielding member having a collimating slot extending from an exterior wall into said bore at the location of said source, and a shutter for said slot formed of radiation absorbing mat\ei'al.

5. A beam forming unit comprising, in combination, a generally spherical shield of radiation absorbing m"- terial, a hollow axle extending through said shield with the ends thereof protruding on either side of said shield to form trunnions for rotatably mounting the same, an elongated source holder removably positioned in said axle, said holder being formed of radiation absorbing material and having a radioactive source positioned intermediate its ends, said shield and axle having a collimating slot extending from an exterior wall into said axle at the location of said source, and a shutter for said slot.

6. Apparatus for forming a beam of radiations from a radioactive source consisting of a shielding member ot radiation absorbing material, a hollow axle extending through said member with the ends thereof protruding on either side of said member to form trunnions for rotatably mounting the same, the opening in said axle being adapted to receive a radioactive source held in an elongated source holder fitting said opening, said shielding member and axle having matching slots forming a single collimating slot extending radially outwardly from the position of said source when in inserted position to an external surface of said shielding member.

7. Apparatus for forming a beam of penetrative radiations from a radioactive source consisting of a generally spherical shield of radiation absorbing material, a hollow axle extending through said shield with the ends thereof protruding on either side of said shield to form trunnions for rotatably mounting the same, an elongated source holder removably insertable in said axle, said holder being composed of radiation absorbing material and having a source holding portion spaced from its ends for holding a radioactive source, the quantity of material between said source holding portion and both ends of said holder being sufficient to reduce the intensity of radiations passing therethrough in an axial direction to a tolerable level, said shield and axle having a collimating slot extending from an exterior wall into said axle at the location of said source holding portion of said holder when said holder is in place inside said axle, and a shutter for said slot composed of radiation absorbing material.

S. A unit for forming a beam of penetrative radiation from a radioactive source consisting ot' a shielding member of radiation absorbing material, a hollow axle extending through said shielding member with the ends thereof protruding on either side of said member, the opening in said axle being adapted to receive an elongated radioactive source holder fitting said opening, said shielding member and axle having matching slots forming a single collimating slot extending outwardly from the position of said source when in inserted position to an external surface of said shielding member.

9. A radiation beam-forming unit consisting of a generally spherical shielding member formed of radiation absorbing material having a central bore extending therethrough, an elongated source holder removably positioned in and fitting said bore and being substantially coextensive therewith, said holder being composed of radiation absorbing material and having a radioactive source positioned intermediate its ends, said shielding member havng a collimating slot extending from an exterior wall into said bore at the location of said source, and a shutter for said slot formed of radiation absorbing material.

10. A radiation beam-forming unit consisting of a generally spherical shield of radiation absorbing material, a hollow axle extending through said shield with the ends thereof protruding on either side of said shield to form trunnions for rotatably mounting the same, an elongated source holder removably positioned within said axle, said holder being formed of radiation absorbing material and having a radioactive source positioned intermediate its ends, said shield and axle having a collimating slot extending from an exterior wall into said axle at the location of said source, and a shutter for said slot.

References Cited in the file of this patent UNITED STATES PATENTS 2,477,648 Piggot et al. Aug. 2, 1949 2,495,781 Silverman Jan. 31, 1950 2,514,909 Strickland July 11, 1950 2,551,491 Gilks May 1, 1951 2,670,443 Pennock et al Feb. 23, 1954 

1. IN A UNIT FOR FORMING A BEAM OF PENETRATIVE RADIACTIONS FROM RADIOACTIVE SOURCE, THE COMBINATION WHICH COMPRISES A GENERALLY SPHERICAL SHIELD OF RADIATION ABSORBING MATERIAL, A HOLLOW AXLE EXTENDING THROUGH SAID SHIELD WITH THE ENDS THEROF PROTRUDING ON EITHER SIDE OF SAID SHIELD TO FORMING TRUNNIONS FOR ROTATABLY MOUNTING THE SAME, THE OPENING IN SAID AXLE BEING ADAPTED TO RECEIVE A RADIOACTIVE SOURCE HELD IN AN ELONGATED SOURCE HOLDER FITTING SAID OPENING, SAID SHIELD AND AXLE HAVING MATCHING SLOTS FORMING A SINGLE COLLIMATING SLOT EXTENDING RADIALLY OUTWARDLY FROM THE POSITION OF SAID SOURCE WHEN IN INSERTED POSITON OT AN EXTERNAL SURFACE OF SAID SHIELD. 